linux-kernel - Re: [PATCH 03/12] mm: Share the anon_vma ref counts between KSM and page migration

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Message-ID: <20100219215826.GF1445@csn.ul.ie>
Date:	Fri, 19 Feb 2010 21:58:26 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Rik van Riel <riel@...hat.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 03/12] mm: Share the anon_vma ref counts between KSM
	and page migration

On Fri, Feb 19, 2010 at 04:42:18PM -0500, Rik van Riel wrote:
> On 02/18/2010 01:02 PM, Mel Gorman wrote:
>
>>   struct anon_vma {
>>   	spinlock_t lock;	/* Serialize access to vma list */
>> -#ifdef CONFIG_KSM
>> -	atomic_t ksm_refcount;
>> -#endif
>> -#ifdef CONFIG_MIGRATION
>> -	atomic_t migrate_refcount;
>> +#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
>> +
>> +	/*
>> +	 * The refcount is taken by either KSM or page migration
>> +	 * to take a reference to an anon_vma when there is no
>> +	 * guarantee that the vma of page tables will exist for
>> +	 * the duration of the operation. A caller that takes
>> +	 * the reference is responsible for clearing up the
>> +	 * anon_vma if they are the last user on release
>> +	 */
>> +	atomic_t refcount;
>
> Calling it just refcount is probably confusing, since
> the anon_vma is also referenced by being on the chain
> with others.
>
> Maybe "other_refcount" because it is refcounts taken
> by things other than VMAs?  I am sure there is a better
> name possible...
>

external_refcount is about as good as I can think of to explain what's
going on :/

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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